I like this idea!! Some of the abilities listed in this thread are actually really unique! I've come up with a few myself too! Let me know which ones ya like!!
So check this out , right?!
Maneuverability: Avoids multi-hit attacks(Fury Attack, Rock Tomb, Bullet Seed, etc.), "Locked in" attacks(Rollout, Thrash, Outrage), 2-turn attacks(Solarbeam unless under sun, Razor Wind, Skull Bash), consecutive attacks in Double/Triple battles(so you won't get "ganged up" on the second attack will always miss unless it's moves like Aerial Ace, Swift, etc.)! Also applies to Beat Up and Pokemon with the
Skill Link ability!!
Examples: Sentret line, Aipom line, Spoink line, Pansage/Pansear/Panpour lines!!
Heavyweight: All physical attacks by user are STAB(no matter what type the attack) but user takes 50% recoil damage. If the attack is already STAB then it gets an additional 1.1x boost!
Examples: Snorlax, Wailmer line, Metagross, Beartic!!
Leech: Steals 1/8 of foe's HP every turn user is in battle!!
Examples: Paras line, Spinarak line, Venipede line, Joltik line
Aerodynamic: Boosts user's Speed after it uses a Flying-type move by one stage!
Examples: Spearow line, Zubat line, Scizor, Taillow line, Latias/Latios
Bloom: Boosts Def & Sp.Def by two stages of all Grass-types in battles! Both user & foe!
Examples: Oddish line, Chikorita line, Lileep line, Shaymin(land forme), Petalili line
Authority: Gives user top priority in battle(even if foe uses priority moves user still strikes first no matter what)!
Examples:Seaking, Kingdra, Slowking, Slaking, Entei/Raikou/Suicune
Energy Boost: Has a 20% chance of raising user & allies' Sp.Atk & Speed if it uses a special attack!!
Examples:Exeggcute line, Espeon, Seedot line, Tropius!
Veil: Prevents any non-direct attacking move from foe(entry hazards, status ailments, stat boosting/reducing moves, etc.)!
Examples: Dratini line, Bagon line, Gible line, Axew line!!
Healing Factor: Heals 1/8 of user's HP every turn it takes damage!!
Examples: Happiny line, Staryu line, Cleffa line, Gardevoir, Celebi, Audino
Girth: Ups user's Attack & Defense by two stages at half it's Max HP!
Examples: Mankey line, Teddiursa line, Makuhita line, Riolu line, Throh
Disability: Prevents foe's ability upon user switching in & already in battle!
Examples: Slowpoke/Slowbro, Shuppet line, Absol, Wyanut line
Reaper: Heals 25% of user's Max HP if foe faints!
Examples: Duskull line, Misdreavus line, Sableye, Murkrow line, Vullaby line, Darkrai
Almighty: User is immune to all physical attacks!!
Examples: Mewtwo, Mew, Deoxys, Rayquaza, Arceus, Reshiram, Zekrom
Phew!! Just what I had at the top of my head! If you know any more examples then be sure to post them yourself!